Ferromanganese crusts from Necker Ridge, Horizon Guyot and S.P. Lee Guyot: Geological considerations

摘要: Abstract Necker Ridge, Horizon Guyot and S.P. Lee in the Central Pacific were sampled, seismically surveyed, photographed by bottom cameras order to better understand distribution, origin, evolution of ferromanganese crusts. Ridge is over 600 km long with a rugged crest, pods sediment 146 m thick, slopes that average 12° 20°, debris aprons cover some lower flanks. Substrate lithologies are mostly hyaloclastite, volcaniclastic breccia, minor alkalic basalt. Guyot, 300 75 wide, capped at least 160 sediment, which buries stepped terraces. similar those on although previous workers sampled much tholeiitic basalt Horizon. 125 80 contains talus along its Ferromanganese-encrusted rocks recovered every dredge thickest Ridge. Crust thicknesses about 2.5, 1.5, 0.8 cm for Necker, Horizon, Lee, respectively. Crusts range from smooth or porous surfaces knobby botryoidal. The entire crust laminated, however, two distinct layers commonly exist, separated paper-thin layer phosphorite. dominant mineral all crusts vernadite (δ-MnO 2 ), while quartz, feldspar, apatite, and, three todorokite, phases. Quartz feldspar decrease decreasing latitude occurrence, suggested be related eolian input. On average, apatite also increases within may high biological productivity zone equatorial upwelling. Phosphorite substrates more abundant than they Guyot. Seamount nodules abyssal their chemistry internal structure.